Severable safety joint for pipe strings



Dec. l6,;l-952. w. foELkE 2,621,395

' I SEVERABLE SAFETY JOINT Folk PIPE STRINGS Filed Dec. 8, 1950 2 Sl-IEETSSHEET 1 I g.\\ M/ INVENTOR.

50 Lester W. Taelke BY ATTORNEY Dec. 16, 1952 2 SHEETS-SHEET 2 Filed Dec. 8, 1950 4 WT .m L T S 3 M E I 3 l w 6 w MM w mi m E M I w\\%y%%/ A Patented Dec. 16, 1952 SEVERABLE SAFETY JOINT FOR PIPE STRINGS Lester W. Toelke, Houston, Tex, assignor to McCullough Tool Company, a corporation of Nevada Application December 8, 1950, Serial No. 199,800

Claims.

This invention relates to severable pipe couplings, commonly termed safety joints, for use in well strings and particularly to a safety joint which is severable by the action of an explosive charge which is initially installed as an integral part of the joint.

The more conventional type of safety joint comprises a threaded couplin which is adapted to be installed in well pipe string, particularly rotary drill strings, the engaging threads of the couplihg members being made relatively coarse to permit unscrewing of the joint preferentially with respect to the more finely threaded ordinary couplings employed in the pipe string. Such joints are normally installed near the lower end of the pipe string, for example, adjacent the drill bit or drill collars of the usual rotary drilling string, so that in the event the drill bit or the lower end of the drill string should become stuck in the Well bore, reverse rotation of the drill string will cause the latter to part preferentially in the safety joint and thus allow the operator to retrieve the major portion of the drilling string.

In many instances, however, the threads of such more conventional safety joints will become galled or will freeze" due to improper handling, infiltration of fluids in the well bore, or other conditions encountered during the drilling. As a. result, the safety joint will often fail to perform the function for which it is intended and prove a source of difliculty and even hazard in the well drilling operations. Also, the joint, being composed of two threadedly engaged coupling members, may, under certain conditions, come unscrewed and thereby sever the drilling string at times and under conditions when such separation is highly undesirable.

Accordingly, the present invention has for its principal object the provision of an improved form of safety joint which will obviate or eliminate the difficulties and disadvantages, as pointed out above, to which the more conventional threaded types of safety joints are subject.

A primary object of this invention is to provide a non-threaded type of safety joint which is severable by means of explosives.

An important object is the provision of a safety joint composed of a tubular body member adapted to form a continuous connection between adjacent pipe sections, the body having mounted in the Wall thereof an explosive charge adapted, when detonated, to sever the body intermediate its ends.

A further object is to provide a tubular body member having an annular explosive charge mounted in the outer wall thereof, said explosive charge being shaped to produce an annular cutting jet directed inwardly toward the bore of said body member.

An additional object is to provide means mounted externally of the body member for sealing the explosive charge against intrusion of well fluids.

Other and more specific objects and advantages of this invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings which illustrate useful embodiments in accordance with this invention.

In the drawings:

Fig. 1 is a longitudinal elevational view of the body member having some portions thereof broken away to better illustrate details thereof;

Fig. 2 is a longitudinal sectional view of the safety joint in accordance with this invention, showing the joint installed in a pipe string;

Fig. 3 is a cross-sectional view along line 33 of Fig. 2;

Fig. 4 is a longitudinal sectional view of the safety joint illustrating its appearance after detonation of the severing charge:

Fig. 5 is a longitudinal sectional view of a drilling strin in a well showing the safety joint located adjacent the bit and one form of detonating device for exploding the charge in the safety joint; and

Fig. 6 is a longitudinal sectional View through portions of a pipe string showing several safety joints in accordance with this invention installed at longitudinally spaced points therein, and showing another means for detonatin the explosive charges.

Referring to the drawings and to Figs. 1 to 3 particularly, there is shown a generally tubular body It) having an axial bore II and provided with an externally threaded pin 12 at one end and an internally threaded socket I3 at the opposite end. The threaded pin and socket may be of standardized dimensions and thread design adapted to form a connection between adjacent sections of a pipe string such as a drill pipe string, so as to form an integral part of such a pipe string, bore II forming a part of the bore of such a string. Body Ill is reduced somewhat in external diameter from a point a short distance above pin l2 to its upper end to thereby form an upwardly facing annular shoulder l4. At a point intermediate the ends of body In and above shoulder It, the external wall of body I0 is provided with a circular groove l5 extending inwardly for about half the thickness of the wall.

A small diameter hole i6 is bored in the outer wall of body In and extends radially inwardly to a point spaced slightly from the wall of bore I, thereby leaving a small thickness of wall metal I! between the inner end of hole l6 and bore I The outer end of hole It communicates with groove l through a slot |8 cut in the outer wall of body Ii]. A pair of packing recesses |9|9 are out circumferentially in the outer wall of body It] above and below groove l5 and are adapted to receive resilient packing rings -20, preferably of the conventional O-ring form. A tubular sleeve 2|, the bore of which is dimensioned to form a close sliding fit over the exterior of body It, is provided to slide downwardly over body Ill from its upper end and to seat on shoulder I4. The exterior diameter of sleeve 2| is dimensioned to be flush with the external diameter of body Ill at shoulder l4, and its length is made such that its upper end will be substantially flush with the upper end of socket |2 when the sleeve is seated on shoulder l4.

Seated in groove I5 is an annular charge 22 composed of a detonating explosive material which is preferably of a high brisance type, such as pentaerythritol-pentanitrate (PETN) trinitrotoluene (TNT), Pentolite (50% PETN and 50% TNT), Tetryl, Amatol, Cyclonite, "Tetrytol or other well known detonating chemicals. The particular explosive material will pref erably be one which will be stable at relatively high temperatures and when subjected to substantial shock. Charge 22 is constructed of two or more arcuate segments for convenient installation in groove IS in forming a complete ring about body In. The thickness of charge 22 will be made such that its outer periphery will be flush with the exterior of body It) When its inner periphery is seated snugly against the inner end of groove I5. The inner periphery of charge 22 is provided with a continuous annular hollow 23 which is of re-entrant form, such that in crosssection it may be triangular, as shown in Fig. 2, or may be arcuate, or frusto-pyramidal, or of any other suitable form commonly employed in forming so-called shaped charges. Hollow 23 is lined with a thin liner 24 of corresponding geometrical shape and may be thin sheet metal such as copper, steel, aluminum, or the like, or plastic, glass or other suitable lining material. Pellets 25, composed of a suitable booster explosive, are disposed in hole l6 and slot 18 to form a continuous booster train which at one end is placed in contact with wall I! and at the other in contact with explosive charge 22. In assembling the safety joint in accordance with this invention, charge 22 equipped with liner 24 will be installed in groove l5, and booster charge 25 will be put in place in hole I6 and slot l8. Seal rings 20 will be installed in recesses l9 and sleeve 2| slipped over the upper end of body Ill pushed down to its seat on shoulder l4. This will complete the assembly of the safety joint, seal rings 20 forming fluid-tight seals between body If! and sleeve 2| to effectively prevent intrusion of fluid from the opposite ends of the device into contact with the explosive material.

In operation the safety joint, assembled as described, will be installed in a well string, such as the usual string of drill pipe, being inserted, as illustrated in Fig. 2, at any desired point in the string between adjacent sections of the pipe 2626, by connecting the pin and socket ends of body In to the corresponding socket and pin ends, 21 and 28, respectively, of the adjacent pipe 58?- tions, which may be the usual tool joint members ordinarily employed for coupling together the ends of sections of a drilling string. When so installed, the safety joint in accordance with this invention becomes for all practical purposes an integral part of the pipe string, corresponding in all ordinary respects to one of the pipe sections composing the pipe string, and will engage in all the ordinary and usual operations of the entire string. Since no special threaded connection is included in the safety joint, the strength and continuity of the string will not be reduced or otherwise efiected in the conduct of the ordinary operations of the string as a whole.

In the event the string becomes stuck in the well at some point below the safety joint, so that it becomes desirable to sever the string at a point above the point at which it is stuck, a charge of a suitable explosive 29 may be lowered through the bore of the string to a point opposite explosive charge 22 and will be set off in any suitable or convenient manner. The high intensity shock resulting from the explosion of such a charge confined in the bore of body l0 will be transmitted through the relatively thin wall section I! into the contacting end of booster charge 25, which will be set off and will transmit its detonating shock to the main charge 22 which will be thus, in turn, set off. By constructing charge 22 in the hollowed form described and by employing a liner for hollow 23, the gases produced by detonation of charge 22 will be caused to converge generally along the axis of hollow 23 to form a thin annular jet of great penetrating power and which will be directed inwardly toward bore ll of bod H1, generally as indicated by the converging broken lines in Fig. 2. The circular jet thus produced will cut through the Wall of body l0 opposite groove l5 and will thereby sever the body cleanly at this point. The portion of the pipe string above the point of severance may then be withdrawn from the well, leaving the lower portion in the well'for recovery or removal by suitable and generally conventional fishing operations. Fig. 4 illustrates the appearance of the safety joint after it has been severed in the manner described and withdrawal of the upper portion of the string has begun.

Various types of explosive arrangements may be employed to set off the main cutting charge 22. Fig. 2 illustrates one convenient arrange ment, in which explosive 29 is a piece of a flexible cord-type detonating explosive, such as the Well known Prima Cord." In this instance the length of cord-type explosive will ordinarily be such as to extend axially the full length of body H). A suitable weighting member 30, of any suitable form and weight will be attached to the lower end of the explosive cord, the upper end of which will be connected to a conventional, electrically fired blasting cap 3|, carried by a firing head 32 suspended from and supported by a lowering cable 33 (Fig. 6) through which an electrical conductor 34 is threaded and extends to the surface where it may be connected to any conventional form of electrical initiator (not shown) by which electric current may be supplied for transmission through conductor 32 to blasting cap 3|. The connection of the detonating cord to blasting cap 3| and the opposite end thereof will be sealed in any conventional manner against intrusion of well fluids. I

As noted, the safety joint in accordance with this invention may be installed at any desired point along a pipe string. In the case of a drilling string, it will usually be located just above the bit, for example, between the bit stem and the first drill collar, since generally sticking of the drilling string will most often occur at the bit because it is usually larger in diameter than the drill collar or drill pipe and forms an upwardly facing shoulder on which cuttings, sand or the like may lodge and thereby stick the drill (see Fig. 5'). It will, therefore, usually be desirable to sever the pipe as near as possible to the bit.

If desired, several safety joints, of the type described, may be installed at longitudinally spaced points along the drilling string, so that the string may be severed at the location of one or the other of these joints, depending upon the point at which the drilling string may become stuck. Fig. 6 illustrates such an arrangement. Since, the location of the several safety joints will be known from the points of their original installation in the pipe string and the length of the string in the well, the explosive for setting off the severing charge in the safety joint may be lowered inside the bore of the string and readily located opposite the safety joint nearest above the point at which the string is stuck and may then be set off to sever the string at the selected joint.

Fig. 5 illustrates another firing mechanism for setting off the severing charge by means of a percussion type go-devil, described in detail in U. S. application, Serial No. 199,660, filed November 8, 1950, by O. J. McCullough. In this arrangement, the piece of cord-type explosive 23 will be connected at its lower end to a weighted firing head 35, having an internal chamber 35. A percussion type blasting cap 37 is connected to the end of the explosive cord as and extends into the upper end of chamber 36. A firing pin 38 is slidably mounted in the lower end wall 39 of chamber 36 in registration with cap 31 and extends below the end of head 35. The outer end of firing pin 33 is provided with an enlarged head 40, and the pin will normally be held retracted from contact with cap 31 by means of a shear pin 4| which extends transversely through the body of firing pin 33 and bears against the lower end of head 35. Since, the drilling string will ordinarily be filled with drilling mud or well fluids or both, means is provided to maintain the length of explosive cord 29 in longitudinally extended position through the safety joint. This means comprises a float l2, of any suitable construction, which is suitably connected to the upper end of cord 29 and is constructed to have sufificient buoyancy to maintain explosive cord 29 in extended position, without offering serious resistance to the sinking of the firing mechanism as a whole through the fiuid in the bore of the drilling string.

When it is desired to sever the safety joint, the firing mechanism is dropped into the bore of the drilling string at the surface and will sink of its own weight through the fluid therein until head 40 of the firing pin comes in contact with the end of the bit stem 43 by which the bit 4 3 is ordinarily attached to the lower end of the pipe string. Upon impact, the inertia of head 35 will break shear pin 4| and drive firing pin 33 against the end of blasting cap 31 setting off cord 29 and thereby providing the detonating shock necessary to set off the main cutting charge 22 to effect severing of the safety joint.

It will be understood that the design or details of the firing mechanism employed for setting off the cutting charge do not, of themselves, form a part of this invention, which is directed primarily to the construction of the severable type safety joint itself. The firing mechanisms described are, therefore, intended to be merelyi1lus trative of various types of such mechanisms which may be satisfactorily used for this purpose.

It will be understood that safety joints constructed in accordance with this invention may be employed in pipe strings of various types, including casing and tubing strings, as well as drill pipe strings. The cutting charges may be arranged to cut outwardly toward the exterior of the pipe, instead of inwardly, as shown in theillustrative embodiment. Although it is. preferable to employ a ring-shaped cutting charge, as described above in the illustrative embodiment of this invention, in order to cleanly sever the safety joint throughout its circumference, other forms and shape-s of charges may be employed which may only partially sever the joint or otherwise weaken it sufficiently that the joint will part or break readily under a moderately strong pull or by rotation of the pipe string sufiicient to twist the joint at the weakened point. Various other alterations and modifications may be made in the details of the illustrative embodiment in accordance with this invention within the scope of the appended claims but without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. A severaole safety joint for pipe strings, comprising, a tubular body member adapted to be connected into a pipe string as a part thereof, and a detonatable explosive charge embedded in the wall of said body member intermediate the inner and outer surfaces of said wall and shaped to at least partially sever said body member when detonated.

2. A severable safety joint for pipe strings, comprising, a tubular body member adapted to be connected into a pipe string as a part thereof, and a detonatable explosive charge embedded in the wall of said body member intermediate the inner and outer surfaces of said wall and shaped to at least partially sever said body member when detonated, said charge being detonatable by detonating shock generated within said bore and transmitted through the: inner surface of said wall to said charge.

3. A severable safety joint for pipe strings, comprising, a tubular body member adapted to be connected into a pipe string as a part thereof, a detonatable explosive charge embedded in the wall of said body member intermediate the inner and outer surfaces of said wall and shaped to at least partially sever said body member when detonated, and a booster explosive train confined within said wall and extending from said charge to a point adjacent the inner surface of said Wall.

4. A severable safety joint for pipe strings, comprising, a. tubular body member adapted to be connected into a pipe string as a part thereof, an annular detonatable explosive charge embedded within the wall of said body member intermediate the inner and outer surfaces of said wall, and an annular hollow in the inner periphery of said charge facing said bore and spaced therefrom, said charge being detonatable by detonating shock. gene-rated within said bore and transmitted through said wall to said charge.

5. A severable safety joint for pipe strings, comprising, a tubular body member adapted to be connected into a pipe string as a part thereof, an annular detonatable explosive charge embedded r 7 within the wall of said body member intermediate the inner and outer surfaces of said wall, an annular hollow in the inner periphery of said charge facing said bore and spaced therefrom, and a correspondingly shaped liner member seated in said hollow, said charge being detonatable by detonating shock generated within said bore and transmitted through said wall to said charge.

.6. A severable safety joint for pipe strings, comprising, a tubular body member adapted to be connected into a pipe string as a part thereof, an annular detonatable explosive charge embedded within the wall of said body member intermediate the inner and outer surfaces of said wall, an annular hollow in the inner periphery of said charge facing said bore and spaced therefrom, and a booster explosive train confined within said wall and extending from said charge to a point adjacent the inner surface of said wall for initially receiving and then transmitting to said charge detonating shock generated within said bore and transmitted through said wall.

7. A severable safety joint for pipe strings,

comprising, a tubular body member'adapted to be connected into a pipe string as a part thereof, an annular groove in the outer surface of said body extending partly through the wall thereof toward the bore of said body, an annular detonatable explosive charge seated in said groove, an annular hollow in the inner periphery of said charge facing said bore, a tubular sleeve slidable over the exterior of said body, and means for sealing the annular space between said sleeve and said body above and below said charge, said charge being detonatable by detonating shock generated within said bore and transmitted through said wall to said charge. a

8. A severable safety joint for pipe strings, comprising, a tubular body member adapted to be connected into a pipe string as a part thereof, an annular groove in the outer surface of said body extending partly through the wall thereof toward the bore of said body, an annular detonatable explosive charge seated in said groove,

an annular hollow in the inner periphery of said 4 charge facing said bore, a correspondingly shaped liner member seated in said hollow, a tubular sleeve slidable over the exterior of said body, and means for sealing the annular space between said sleeve and said body above and below said charge, said charge being detonatable by detonating shock generated within said bore and transmitted through said wall to said charge.

9. A severable safety joint for pipe strings, comprising, a tubular body member adapted to be connected into a pipe string as a part thereof, an annular groove in the outer surface of said body extending partly through the wall thereof toward the bore of said body, an annular detonatable explosive charge seated in said groove,

an annular hollow in the periphery of said charge facing said bore, a correspondingly shaped liner member seated in said hollow, a tubular sleeve slidable over the exterior of said body, means for sealing the annular space between said sleeve and said body above and below said charge, and a booster explosive train confined Within said wall and extending from said charge to a point adjacent the inner surface of said wall for initially receiving and then transmitting to said charge detonating shock generated within said bore and transmitted through said wall.

.10. A severable safety joint for pipe strings, comprising, a tubular body member adapted to be connected into .a pipe string as a part thereof, a ring-shaped hollow explosive charge embedded in the wall of said body member intermediate the inner and outer surfaces of said wall and shaped to sever said body member when detonated, and a separatedetonating explosive body insertible into said bore adapted to generate therein detonating shock transmittable through said wall to said hollow charge for detonating the same.

LESTER W. TOELKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,305,261 Kinley Dec. 15, 1942 2,436,036 Defenbaugh Feb. 17, 1948 2,506,836 Kaltenberger May 9, 1950 

